Soil applied potassium (K) may not alleviate K deficiency in fine textured California soils when high numbers of prunes per tree are produced leading to leaf necrosis and limb death. Because K demand is increased by fruit, K nitrate (KN) sprays appear to be a corrective option for growers in this situation. Our objectives were to determine best seasonal KN spray liming strategies to minimize K deficiency, quantify K uptake into leaves after spray and to evaluate spray effects on productivity. Results indicated that regardless of spray timing leaf K was increased by approximately 0.3% and three weeks later decreased 0.2%. Average leaf K in sprayed trees was 0.7% higher than untreated trees at harvest. Fruit fresh to dry weight ratios were lower (better) from summer sprayed trees than spring. Summer KN sprayed trees had yield efficiencies equal to those having soil applied K. Fruit size was similar regardless of K application method. Foliar KN sprays may be a viable K augmentation to soil application in heavy crop years on fine textured soils.
S.M. Southwick, W. Olson and J. Yeager
Stephen M. Olson and Joe W. Noling
Methylbromide is the standard fumigant used for tomato production in Florida. Since it been classified as a category 1 ozone depleter and is to be phased out by 1 Jan 2001 replacement methods of fumigation must be found. Several materials in 1993 were compared to methylbromide in production of `Colonial' tomatoes. These included metham sodium (applied through drip at 3 rates and applied to soil at 935 l·ha-1 and tilled in), dazomet (applied at 2 rates and tilled in), 1,3 dichloropropene + chloropicrin and untreated check. None of the treatments were as effective as methylbromide in reducing root galling by root knot nematodes. Total yields were not affected by treatments even though root system of untreated plants was severely galled. Modifications are to be made for 1994 season and materials added to trial.
Denise L. Olson, James. R. Nechols and Charles W. Marr
A survey conducted at farmers' markets in eastern Kansas showed that more consumers purchased pumpkins for jack-o-lanterns than for cooking. One to four jack-o-lantern pumpkins are purchased annually per consumer. Whether or not the pumpkins are treated with insecticides to control squash bugs and regardless of their intended use, consumers preferred U.S. no. 1 grade, which sell at the higher retail price of $0.33/kg. At least 90% of the consumers surveyed would pay 20% more than the retail price for insecticide-free pumpkins. About two-thirds of those polled would pay 30% more. Cost-benefit data indicate that the higher prices consumers would pay may not be sufficient for growers to produce insecticide-free pumpkins economically using only biological control. However, if biological control is integrated with host-plant resistance, the higher prices may be sufficient for growers to produce insecticide-free pumpkins.
Dan O. Chellemi, Stephen M. Olson and John W. Scott
Five strains of Pseudomonas solanacearum, collected from northwest Florida tomato fields, were inoculated onto 23 tomato (Lycopersicon esculentum) genotypes and one tomatillo (Physalis ixocarpa) genotype using a stem puncture technique. The strains represented a diverse group based upon pathogenic aggressiveness and profiles of their fatty acid content. Resistance was evaluated by comparing the response of each genotype to susceptible controls consisting of L. esculentum cv Bonny Best and Sunny. A differential response by the genotypes to the individual strains was observed. Germplasm from Hawaii (H7997 and H7998) exhibited some resistance to one of the strains while germplasm from Taiwan (CL 5915-93-1-0-C-1) was moderately resistant to another strain. However, no genotype was resistant to all five strains tested.
John W. Scott, Stephen M. Olson and Jerry A. Bartz
Denise L. Olson, Ronald D. Oetting and Marc W. van Iersel
Coconut coir dust is being marketed as a soilless medium substitute for sphagnum peat moss that inhibits fungus gnat (Bradysia sp.) development. However, little information is available on the effects of coconut coir dust on Bradysia sp. In a laboratory study we examined the effect of substituting coconut coir dust for peat moss, with or without a food source, on the development of fungus gnats. An average of less than one adult emerged when 20 fungus gnat eggs were provided with pure or sterilized peat moss or coconut coir. A significantly higher number of adults (11.5-13) emerged when a food source of 1 g of yeast was added to either soilless potting medium type. The adults required up to 10 fewer days to emerge when food was provided, compared to sterilized and pure media, except for the pure peat moss. In a greenhouse study examining the effects of coir and peat at different textures and different moisture levels on fungus gnat survival, there were significant differences at the different levels of moisture. There was a higher population of larvae in the coarse medium containing peat. In the coir-based media, the fine-textured medium had the highest population level of fungus gnats. There were no significant effects on fungus gnat populations among the different levels of moisture within a medium type. However, there was a tendency for lower populations in the most moist and the driest media and the highest survival in the media that were maintained at 52.5% moisture. Plant growth was best in the media with the lowest number of fungus gnats (coarse coconut coir dust-based and fine and medium peat-based media). These results suggest that it is possible to select growing media that minimize fungus gnat populations, while optimizing plant growth. However, contrary to claims made by growing media producers, coconut coir dust does not necessarily inhibit fungus gnat development.
V.S. Polito, K. Pinney, R. Buchner and W. Olson
We investigated the basis for fruit drop in walnut (Juglans regia L.) following bloom period applications of streptomycin as a potential control treatment for walnut blight, a bacterial disease incited by Xanthomonas campestris pv. juglandis (Pierce) Dye. Experiments were conducted on streptomycin-treated field plots of `Vina' walnut. Four streptomycin treatments were applied at different times relative to anthesis. Fruit from all treatments grew similarly for four weeks following anthesis when high levels of fruit abscission began to occur in the treatment sprayed during the bloom period. Microscopy revealed that in this treatment ovules failed to develop normally, and neither embryo nor endosperm developed. The pattern of fruit development and timing of fruit drop following streptomycin treatment at bloom is similar in all ways to that of unpollinated walnut flowers where growth appears normal until abscission occurs 3 to 5 weeks after anthesis. Pollen germination and pollen tube growth were inhibited in the bloom-period treatments. Pollen germination in vitro was not affected by addition of streptomycin to a germination medium. If streptomycin were to be used in a walnut blight control program, application timed to coincide with the period of pistillate bloom and pistillate flower receptivity should be avoided.
S.M. Southwick, W. Olson, J. Yeager and K.G. Weis
During the fruit growing season, April through August 1990, 1991, and 1992, four sprays of 20-22 liters/tree of KNO3 were applied to `French' prune trees (Prunus domestica L. syn. `Petite d'Agen). Spray applications of KNO3 were compared to single annual soil applications of KCl (1.4-2.3 kg/tree) and sprays of urea + KNO3 with respect to leaf K and N, fruit size, drying ratio, and dry yield. Potassium nitrate sprays were as effective, or better, than soil-applied K in maintaining adequate levels of leaf K throughout the season. Treatment effects were not carried over into the next year. Lowest leaf K was found in trees where no K had been applied. Those values were below the adequate level of 1.3% K and the untreated group developed K deficiency symptoms. Consistent effects on leaf K were not obtained when urea was applied and no negative effect on leaf K was demonstrated. Equivalent dry yields per tree were obtained by foliar and soil K applications. There was no best time for KNO3 sprays. Yield per tree was not enhanced when foliar K-N sprays were applied to trees that had levels of 1.3% K or more as of 15 Apr. 1992. Trees that were below optimum K in April tended toward improved dry yields after four K-N sprays. Trees that had no applied K were lowest yielding. Drying ratios and fruit size (number of fruit per kilogram) were not different among K treatments. Dry yields per tree were increased without a decrease in fruit size or an increase in drying ratio with either soil or foliar K application. These results suggest that foliar KNO3 sprays applied four times throughout the growing season can be used to correct incipient K deficiency in `French' prune and to obtain dry yields equivalent to those obtained with soil applications of KCl.
J.W. Scott, J.B. Jones, G.C. Somodi, D.O. Chellemi and S.M. Olson
David G. Riley, Shimat V. Joseph, W. Terry Kelley, Steve Olson and John Scott
Commercially available cultivars of tomato Solanum lycopersicum L. were field-tested for resistance to Tomato spotted wilt virus (TSWV) over a 5-year period (from 2006 to 2010) at the Coastal Plain Experiment Station at Tifton, GA. Selected cultivars were transplanted each year into staked, black plastic mulch beds on drip irrigation in the spring of each year when the incidence of Tomato spotted wilt (TSW) tended to be highest. The presence of TSWV was confirmed by double antibody sandwich (DAS) enzyme-linked immunosorbent assay (ELISA). Also, the presence of thrips vectors was monitored using beat-cup sampling of foliage and flower samples. Tomato cultivars with the Sw-5 resistance gene provided high levels of control of TSW expression over all 5 years. However, these genotypes had no apparent effect on the thrips vectors, western flower thrips, Frankliniella occidentalis (Pergande), and tobacco thrips, Frankliniella fusca (Hinds), that transmit TSWV. Overall, the top 15 commercial tomato cultivars based on consistent TSW resistance and ranked from highest marketable fruit yield were: ‘Tycoon’, ‘Tous 91’, ‘Talladega’, ‘Red Defender’, ‘BHN 444’, ‘Nico’, ‘Carson’, ‘BHN 685 (Roma type)’, ‘Picus’, ‘Redline’, ‘Tribute’, ‘Quincy’, ‘BHN 640’, ‘BHN 602’, and ‘Top Gun’.